High molecular weight, water-soluble and water-swellable polymers produced from such monomers as acrylamide are commercially important materials. These polymers find use as flocculants for mining operations to recover ore from slurries, water treating to remove suspended impurities etc., in agriculture as soil conditioners, and also in paper making to aid paper formation and in oil recovery industries.
Water-soluble and water-swellable polymers are generally commercially available in solution, dry, dispersion, water-in-oil emulsion, and water-in-oil microemulsion forms. In many cases polymer solutions are convenient, but may be limited to low molecular weight polymers and/or low solids levels because of the problem of handling viscous solutions of high solids, high molecular weight polymers. At very high solids and/or molecular weights, the solutions form gels that can be comminuted to form fine polymer gel particles that may be dissolved into water by the end-user. Although these comminuted gels typically contain up to about 20% water, they are frequently called "dry" polymers to distinguish them from the other product forms. In many cases the dry polymers exhibit long dissolution times and poor handling characteristics e.g. dusting. Although some handling problems may be mitigated by agglomeration see e.g. EP 0 277 018 A2; U.S. Pat. Nos. 3,279,924; 3,275,449, 4,696,762; 5,171,781; both solutions and gels of water-soluble and water-swellable polymers may also suffer from the lack of a convenient method for post-reacting or functionalizing the polymer.
Another problem relates to blends of dry polymers, particularly when blending dry polymers having different particle sizes or particle size distributions. It is well known that dry polymer particles tend to stratify on handling and storage, with the larger particles tending to settle towards the bottom of the container, and the smaller particles tending to be concentrated towards the top. Stratification may be inconvenient because differences in handling characteristics are encountered as a function of container depth. The stratification problem may be exacerbated when two different dry polymers are blended together, because the particle size distributions of the two products are generally not identical. Stratification on storage may affect blend product performance as the top of the container tends to become enriched in the polymer having the smaller particle size. For obvious reasons, changes in product performance as a function of storage depth are to be avoided, and it is generally preferred that each polymer be of similar particle size, see e.g. EP 479 616 A1 and U.S. Pat. No. 5,213,693. However, when producing dry polymer by spray-drying, changes in production e.g. changes in dryer size, dryer temperature, bulk viscosity of the feed, atomizer type, etc. may affect particle size, and it may be difficult or impossible to achieve a desired particle size while simultaneously maintaining some other production parameter, so blends of spray-dried polymers may be adversely affected by stratification.
The advent of water-in-oil emulsion and water-in-oil microemulsion forms of water-soluble and water-swellable polymers solved some of these problems, e.g. blends of water-in-oil emulsions and water-in-oil microemulsions as disclosed in U.S. patent application Ser. Nos. 08/157,764 and 08/157,795 do not tend to stratify, and high solids, high molecular weight, and relatively fast dissolution times may all be obtained simultaneously. In addition, unique functionalized polymers may be produced that cannot be practically manufactured by polymerization in solution. For instance, U.S. Pat. Nos. 4,956,399; 4,956,400; 5,037,881; and 5,132,023, teach that functionalization of a water-soluble polymer contained in a water-in-oil microemulsion can be carried out to produce high molecular weight charged polymers with advantageous flocculation performance. The use of microemulsions, as opposed to emulsions, in polymer production provides improved polymer performance properties among other benefits. Hydrolyzed polyacrylamides with uniquely high molecular weight are disclosed in U.S. Pat. No. 5,286,806. In U.S. Pat. No. 4,767,540, very high molecular weight hydroxamate-functionalized polyacrylamide is disclosed, and novel charged organic polymer microbeads are disclosed in U.S. Pat. Nos. 5,274,055 and 5,167,766. In addition, methods for esterifying (meth)acrylic acid polymer and, optionally, hydroxamating said polymers are disclosed in U.S. patent application Ser. No. 08/626,297.
Despite the many benefits provided by emulsion and microemulsion polymers, transportation costs associated with such materials remain high and disposal of the oil and emulsifier in the emulsions may pose environmental concerns as secondary pollution. Moreover, many emulsion and microemulsion polymers tend to exhibit stability problems, e.g. detrimental changes in polymer properties and/or performance as a function of time. Although U.S. Ser. Nos. 08/157,764 and 08/157,795; and U.S. Pat. Nos. 4,956,399; 4,956,400; 5,037,881; 5.132,023; 5,274,055; and 5,167,766 mention non-solvent precipitation and stripping as methods of recovering dry polymer products from water-swellable or water-soluble polymer microemulsions or microemulsion-containing blends, these methods may produce a dry polymer with undesirable handling properties, poor dissolution times, low bulk density, etc. Practically, non-solvent precipitation and stripping may be inconvenient and expensive.
Water-soluble polymers may also be prepared in the form of suspensions or dispersions of polymer beads or droplets in a non-aqueous liquid e.g. oil. The reverse phase polymerization process described in U.S. Pat. No. 4,528,321 is said to form dispersions of water-soluble polymers. Water-soluble polymer dispersions, which may be azeotropically dried, are disclosed in U.S. Pat. No. 4,628,078. U.S. Pat. 4,506,062 discloses a reverse phase suspension polymerization process for the production of high molecular weight, water-soluble polymers and also reports that dry polymer beads may be obtained by azeotropic evaporation followed by filtration. However, a problem remains in that azeotropic distillation tends to be energy-intensive, and the filtering process may be hazardous or inconvenient.
Although dry polymers may be obtained from vinyl-addition polymer-containing water-in-oil emulsions, water-in-oil microemulsions or dispersions by such methods as precipitation in a non-solvent, stripping, etc., these methods may also be impractical lor economic and environmental reasons because of difficulties in recovering, purifying and recycling the oil. Although the oil recovered from an emulsion or suspension polymerization may occasionally be recycled without further purification, as disclosed in U.S. Pat. No. 4,212,784 and JP 50-124979, in other cases e.g. S.I.R. H915 additional purification steps are necessary. The level of impurities in the oil is an important consideration, as certain polymerizations e.g. chain-growth polymerizations, or polymerizations used to make very high molecular weight polymers, are especially sensitive to even trace amounts of polymerization-debilitating substances. Particular problems are also encountered where the polymer has been formed from monomers in the presence of the oil or the oil has been heated or subjected to processing steps, which may have a tendency to deposit polymerization-debilitating impurities in the oil.
Spray-drying is the transformation of feed from a fluid state to a dried particulate form by spraying the feed into a hot drying medium, typically a hot gas. Spray-drying is widely used to produce a diverse range of products e.g. instant coffee, dried eggs, instant milk, household detergents, pharmaceutical products, pigments, cosmetics, starch, plastics, ceramics, etc. Typical spray-drying equipment, drying procedures, etc. are described in detail in known references e.g. "Spray Drying Handbook," by K. Master, 5th Ed., Longman Scientific, 1991.
Aqueous solutions of water-soluble polymers may be spray dried as in U.S. Pat. Nos. 3,803,111 and 4,892,932. U.S. Pat. Nos. 4,847,309 and 4,585,809 disclose processes for spray-drying acrylic polymer-containing emulsions, U.S. Pat. No. 4,798,888 discloses a process for spray-drying a polysaccharide emulsion, U.S. Pat. No. 4,816,558 discloses a process for spray-drying an aqueous dispersion of a synthetic resin and U.S. Pat. No. 4,112,215 discloses a process for spray-drying an aqueous dispersion of a copolymer. U.S. Pat. No. 5,025,004 discloses a process for spray-drying an emulsion of a water-insoluble polymer.
U.S. Pat. No. 4,035,317 teaches that water-in-oil emulsions of water-soluble vinyl-addition polymers may be spray dried, under certain conditions, to produce free-flowing, non-dusting polymer particles which rapidly dissolve in water. Powders of polyacrylamide, acrylamide/acrylic acid copolymer, and acrylamide/dimethylaminopropyl methacrylate copolymers are described therein. The size range of the spray-dried products is such that none are smaller than about 325 mesh (about 40 microns), at least about 50% are larger than about 120 mesh (about 122 microns), and substantially none of the particles are larger than about 20 mesh (about 841 microns). These particles do not clump when added to water and dissolve much faster than traditional dry or gel particles of water-soluble polymers. When the spray-dried particles are either larger or smaller than this size range, however, they dissolve with difficulty. Although the invention of U.S. Pat. No. 4,035,317 was a significant advance in the art, a difficulty nevertheless remains with respect to certain polymers, in that the spray-drying methods of said patent gives polymers whose properties are undesirably changed relative to the emulsion or microemulsion form. Attempts to spray-dry Mannich polyacrylamides according to the teachings in the art resulted in polymer powder exhibiting reduced flocculation performance, compared to that of the corresponding polymers used in the microemulsion form. Furthermore, the viscosities of solutions of the spray-dried products tended to be significantly lower than desired.
Accordingly, there exists a need for a method of recovering water-soluble and water-swellable polymers from dispersions, water-in-oil emulsions or water-in-oil microemulsions to produce rapidly dissolving water-soluble polymers without adversely affecting polymer properties. It would also be advantageous to provide blends of two or more spray-dried dry polymers and methods for production thereof wherein 90% or greater of the particles in the blend are each individually comprised of two or more polymers, so that the effect of stratification on the blend is minimized. There also exists a need for an economical method for producing substantially dry polymers having good handling and dissolution properties. It would also be advantageous to provide methods for spray-drying dispersions, water-in-oil emulsions and water-in-oil microemulsions which eliminate or reduce undesirable product changes, and enable component recycling or reuse.
A method has now been discovered for producing substantially dry water-soluble and water-swellable vinyl-addition polymers by spray-drying the corresponding polymer dispersion, water-in-oil emulsion, or water-in-oil microemulsion. Surprisingly, novel dry polymer products are obtained whose properties and/or performance are not detrimentally changed by the spray-drying process. Surprisingly, substantially dry polymers produced by methods of the instant invention tend to have improved stability relative to the corresponding dispersion, water-in-oil emulsion, or water-in-oil microemulsion polymers. Advantageous blends of two or more spray-dried dry polymers and methods for production thereof are also provided, wherein 90% or more of the particles in the blend are each individually comprised of two or more polymers. Surprisingly, the dissolution and handling characteristics of the spray-dried polymer particles of the instant invention are improved by agglomeration. Methods of using the instant compositions of polymer particles and agglomerates in water-treating, paper making, mining, oil, and agricultural industries are disclosed. In further embodiments of the invention, the oil phase of the water-in-oil emulsion or water-in-oil microemulsion is recovered, and purified in another embodiment, said oil phase being surprisingly substantially free of polymerization-debilitating substances.
All patents, patent applications, books, and articles mentioned herein are hereby incorporated by reference.